This article examines the relationship between action research and policy and the kind of confidence teachers, policy makers and other potential users may have in such research. Many published teacher action research accounts are criticised on the grounds that they do not fully meet the conventional standards for reporting social scientific research, and by implication are held to be less trustworthy. Action research is nevertheless often seen by some academics and policy makers as a potential method for developing theory, disseminating good practice, or raising standards. Through a discussion of three major approaches to action research—seen variously as professional learning, practical philosophy and critical social science—it is argued that judgements about confidence depend upon understanding the various kinds of knowledge claim that can be made by action researchers, and appropriate judgements concerning the strength of evidence or reasons.